Stunned audiences were left checking their hearing as the 19-year-old escaped the sing-off for next week's show.
Boyband The Risk, one of Tulisa's groups, were voted off first before the sing-off in the shock elimination.
The group were thought to be safe, but acts criticised by the judges pipped them to be taken through to next week.
It meant that votes on the night left Johnny and Kitty to fight it out for survival.
Johnny, 45, sang the Everly Brothers' Unchained Melody using his unique falsetto to great effect.
Kitty, 26, looked sombre as she sang Kelly Clarkson's Beautiful Disaster but belted out the tune confidently.
But in the end the first three judges decided to save Kitty, powering her through to next week's show.
Johnny was gracious in defeat: "I really want to thank everybody that's got behind me.
"All of you out there, everybody in the UK that accepted me just for being me."
Louis was tearful as he had to choose between his remaining two acts to go.
He said: "I love both acts, they have been incredible to work with.
"I have to pick the person I think in the real would would get a recording contract.
"The act I have to send home tonight is Johnny."
Tulisa agreed, adding: "I get along with both of you guys really well.
"For me the act I'm sending home tonight is Johnny."
And Kelly, despite always calling the high-voiced singer her "guilty pleasure", also gave him the boot.
She said: "Whose album am I going to buy, who am I going to see in concert.
"The act that I'm sending home tonight is Johnny."
Celebrities were outraged by what had happened and said they were switching off the show.
Wayne Rooney tweeted: "Just turned X Factor off. Disgraceful 1st time I've ever refused to watch it. Bring Simon back."
Cricketer Michael Vaughan added: "That's it... My X factor watching career is over...Joke."
Michael Owen fumed: "I'm being subjected to X Factor. Is Louis the biggest nugget of all time? Crying?
"I hate this programme with a passion. All phonies."
The double elimination saw the two acts follow in the footsteps of Sophie Habibis who was voted off last time.
An extraordinary Saturday night of performances saw even more bust-ups among the judges.
Gary and Louis told each other to shut up, while Kelly blasted the Irish judge for telling Frankie Cocozza he would "never be a rock star".
Marcus received most of the praise for his incredible version of Jackie Wilson's classic Reet Petite.
But it was Frankie and Janet who came under fire for their respective versions of Black Eyed Peas' I've Got a Feeling and I Want You Back by the Jackson 5.
Florence and the Machine and JLS all performed during the Sunday extravaganza.
